But imagine you're a bear and can just bust out a window and go in and grab the pie. And now not only is your pie eaten, but you have a bear in your house.

Not only do you need to lock the pie up, you need to hang it from a rope from a tree such that a bear cannot access it, sufficiently far from the campsite that the bear is not presenting a danger to you/others. Keep in mind that bears can climb trees.